The present invention relates to methods for aggregating suspended solid particles in an aqueous medium involving mixing the aqueous medium with an effective amount of a flocculant obtained from animal blood to aggregate the suspended particles, making them easier to separate from the aqueous medium.
Approximately nine billion chickens, 114 million hogs, and 17 million cattle are slaughtered in the U.S. per year (Agriculture Statistics Board, 2009, National Agricultural Statistics Service, U. S. Department of Agriculture). Due to limited demand, income from selling chicken blood (CKB) is not sufficient to cover costs for capturing and processing the blood, and the blood is treated as waste. The CKB, diluted with processing water, is partially treated to remove solids before discharge into the environment. Blood from meat processors is transferred to renderers who prepare blood meal. However, rendering plants are closing due to the reduction of user demand, and rendering plants are now charging a disposal fee for blood (Mittal, G. S., Bioresource Technology, 97: 1119-1135 (2006)). It would be beneficial to chicken and red meat processors if an additional income stream could arise from development of processes that convert CKB, bovine blood (BB) and porcine blood (PB) to useful products. In addition, removal of blood for product preparation would reduce environmental pollution.
A flocculant is a substance that causes suspended particles to aggregate and form discrete flocs (Krishnan, S. V., and Y. A. Attia, Polymeric flocculants, In: Somasundaran, P., Moudgil, B. M. (Eds.), Vol. 27, Surfactant Science Series, Reagents in Mineral Technology, Marcel Dekker, Inc., New York, pp. 485-518 (1988)). Aggregation of the fine particles usually results in accelerated sedimentation to give a clarified solution. Many flocculants are polymeric, and they are used in a wide variety of processes such as wastewater clarification (Maximova, N., and O. Dahl, Curr. Opin. Colloid Int. Sci., 11: 246-266 (2006)), paper manufacture, concentration during chemical operations, and dewatering and thickening in mineral operations (Swarovsky, L., Solid-liquid separation, 4th edition, Butterworth-Heinemann, Oxford, p. 126). They are also used as filtration and centrifugation aids (Lewellyn, M. E., and P. V. Avotins, Dewatering/filtering aids, In: Somasundaran, P., Moudgil, B. M. (Eds.), Vol. 27, Surfactant Science Series, Reagents in Mineral Technology, Marcel Dekker, Inc., New York, pp. 559-578 (1988)).
The most widely used polymeric flocculant is anionic polyacrylamide (PAM) because of its high effectiveness and low toxicity to aquatic life (Nasser, M. S., and A. E. James, Effect of polyacrylamide polymers on floc size and rheological behaviour of kaolinite suspensions, Colloids and Surfaces A: Physicochem. Eng. Aspects, 301: 311-322 (2007)). PAM is also applied directly to soil to prevent erosion in agricultural and construction areas (Sojka, R. E., et al., Advances in Agronomy, 92: 75-162 (2007)).
PAM is manufactured from chemicals that are made from natural gas, so it is expected that the price of PAM will rise over time as supplies of natural gas are depleted. Thus, renewable, biodegradable replacements are being sought. Toward this goal, derivatives of amylopectin, carboxymethylcellulose, guar gum, starch, and glycogen have been tested as flocculants (Pal, S., et al., Colloids and Surfaces A: Physiochem. Eng. Aspects, 289: 193-199 (2006)). Derivatives of chitosan have been examined as coagulation/flocculation aids in waste water treatment (Renault, F., et al., Eur. Polym. J., 45: 1337-1348 (2009)). Extracellular biopolymeric materials from microorganism fermentation have recently been investigated as a new source of renewable flocculants (Salehizadeh, H., and S. A. Shojaosadati, Biotech. Adv., 19: 371-385. (2001)). Additionally, suspensions of chitosan, starch xanthate, cellulose xanthate, and acid-hydrolyzed cellulose microfibrils have been tested for control of soil sediment runoff (Orts, W. J., et al., Industrial Crops and Products, 11: 19-29 (2000)). Known renewable flocculants and erosion control agents generally must be used at significantly higher concentrations than PAM to achieve equivalent results.
We have found that flocculants obtained from animal blood can be used as a biodegradable replacement for PAM.